Many things can happen between firing or launching of a projectile and the eventual completion of its flight. It may simply be "spent" or it may be intended to hit or come into close proximity with a target. It may be intended to explosively damage or disable the target.
If the projectile is simply aimed, fired and travels ballistically, with no flight information detection or control being exercised, there is little more to do but aim and fire until the desired results are achieved. If the projectile is controllable to some extent, or if flight characteristic information is desired, other factors come into play. Flight information may be obtained from radar or by information from an onboard transmitter to a receiver on a remote platform. There may be an active guidance system on board the projectile which could include an active transmitter/receiver system. There may be other types of signal exchange between the projectile and a remote platform associated with the launch site, or between the projectile and the target. Many of these signal transmissions or exchanges could be subject to countermeasure efforts to deflect the projectile from its intended path.